1. Field of the Invention
The present invention relates to a fire extinguishing system, More specifically, the present invention relates to improvements, new configurations and new applications for the thin, breakable panels containing dry chemical fire extinguishant, as disclosed in U.S. Pat. No. 5,762,145, typically for use in various transportation applications.
2. Related Art
A device known as a “powder panel” has been disclosed as a rigid or semi-rigid panel (or system of panels) that could be mounted onto the wall of an aircraft fuel tank adjoining and facing an adjacent bay (U.K. Patents 1,454,493 and 1,547,568). These panels, when impacted by a ballistic projectile penetrating through the aircraft, would rupture locally and release a portion of the extinguishant into the adjacent bay, extinguishing instantly the ignition of fuel sprays originating from the damaged fuel tank when contacting hot incendiary particles from the projectile. These panels were demonstrated with a variety of extinguishing gases and dry chemical powders. These panels took the form of hollow panels with cylinders or sachets of extinguishant inserted, or balls or sheets of reticulated foam (sometimes sealed in bags with pressurized gaseous extinguishant). These panels could be parasitically added in retrofit or integrally built into the aircraft structure. All of these evolutionary improvements to the basic panels showed some level of performance enhancement for a given system volume or weight, but could be offset by increased complexity or increased material, assembly or installation cost. In full scale ballistic testing, various configurations have demonstrated successful fire suppression against various threats, but their performance changed as conditions, threats, or compartment configurations changed. The most common panel configurations were thin panels with a hexagonal honeycomb sandwich material of kraft paper, aluminum or Nomex, filled with a fire extinguishing powder and covered with a thin sheet on both faces of aluminum foil, composite fibers or other materials. Such panels would have to be made thicker (if they worked at all) for certain threats such as small caliber projectiles, which limited the extent of local damage to such panels and the resultant amount of powder discharged to extinguish any fires. This minimal panel damage and discharge was due to the ductility of the outer face materials used, which constrained the local face tearing and the ability for the panel's total powder content to be released. Powder panels have some use on current military aircraft, with various trade-offs present versus the use of regular fire extinguishing systems for these applications. This limitation in discharging its total dry chemical content (and resultant required increase in panel thickness and weight) has limited its favorable implementation for many applications versus other alternatives. Variations of this concept were investigated for use against ballistic impacts in armored vehicles (U.S. Pat. Nos. 3,390,541 and 4,132,271), although powders were primarily limited for use in engine compartments due to the inhalation difficulties with crew members, and gaseous extinguishant filled panels were used in the crew compartment. Since weight reduction was the critical factor for military aircraft, special complex, low production prototype systems were considered for use; the considerable cost of materials, assembly and installation of such configurations and exotic extinguishants were not as strong a factor. For military applications it was understood that the total number of units manufactured would be relatively small and costly in comparison to commercial applications, as is common with specialized military equipment.
Crouch (U.S. Pat. No. 2,911,049) discloses a container mounted of a firewall of a vehicle, containing a fire extinguishing chemical inside. An internal flexible rod is suspended vertically within the extinguishing chemical, with a body of significant mass mounted on its end to resemble a pendulum in configuration. When the vehicle decelerates rapidly (such as in a crash), the inertia of the suspended mass will cause it to impact the wall of the mounted container, rupturing it and allowing the dispersal of extinguishing agent The device must experience sufficient deceleration to activate (thus possibly missing activation in low speed crashes), or undesirably break up and disperse its contents under mere hard braking conditions and small incidental impacts. It can also be limited in the location where it can be mounted in bulk form, which may be at locations where it is hard to reach the location of the fire. The fracture of the container may be incomplete and impede the discharge of the total extinguishing chemical contents. If such contents are pressurized, then special high cost and weight materials and sealing means are required to contain the chemical inside during normal operations.
Lee et al (U.S. Pat. No. 4,251,579) discloses a thin panel comprising two thin face sheets, a honeycomb sandwich material and an extinguishing chemical stored inside. The materials of the components were disclosed to include aluminum, stainless steel, resin-impregnated fiber (such as Fiberglass), and woven or non-woven fibrous material (such as Nomex). These constructions required significant fabrication and layup stages to assemble a panel, which could be quite expensive in terms of labor costs for full-scale commercial production. Such assemblies always featured cellular sandwich materials, with such cells (such as hexagonal honeycomb cells) having an axis penetrating both openings of each cell in a perpendicular direction to the planes of the sheet faces. Such face sheet materials in consideration were quite ductile and were designed to tear locally at the point of impact as opposed to shattering in their entirety. Only “projectiles” were disclosed as an initiating means for these panels, and these panels were disclosed as flat or “bendable” flat panels, designed to be placed near a fuel tank to extinguish fires exclusively.
Bennett (U.S. Pat. No. 5,762,145) discloses the design and use of thin, flexible panels that are hollow, with internal structural members forming channels to give the panels some structural rigidity. These panels are filled with dry chemical fire extinguishing powder and sealed. The panels are mounted in regions near reservoirs of flammable fluids, typically on various forms of transportation such as highway vehicles. One of the most common applications would be their mounting on the exterior walls of fuel tanks of vehicles. When the vehicle so outfitted experiences a severe collision while operating on the road, such that the fuel tank is impacted sufficiently to rupture the fuel tank or related connections, the panels mounted on the fuel tank exterior will also rupture. This panel breakage occurs since any impacting force must first penetrate the exterior panels to contact the fuel tank behind the panels. The dry chemical extinguishing powder is thus released in the form of an expanding cloud, due to the energy applied to the powder from the impacting force and the breakage of the panels. This dry chemical powder is very effective in preventing the ignition of the fuel vapor and mist released from the tank rupture, or quickly extinguishing any incipient ignition sites before they grow into established fires. The design of Bennett (U.S. Pat. No. 5,762,145) features design enhancements over prior art by (1) disclosing a means of forming such powder panels in a more economical manner than previously available, (2) disclosing a design that facilitates a more complete fracturing of the panel to optimize the near full discharge of the entire content of powder from a given panel, and (3) proposing a new means of initiating the panel, by means of impact forces due to a collision of a highway vehicle.
The disclosure of Bennett (U.S. Pat. No. 5,762,145) does feature these enhancements, but additional new designs suited for additional applications and alternative vehicle fire scenarios are desired but were not disclosed. As examples, techniques to protect other fire scenarios, such as collisions impacting and fracturing fuel tank valves and their connectors, particularly for alternate fueled vehicles, are desired but not previously disclosed. Additional flammable fluid reservoirs, such as brake master cylinders and fuel pumps, contain sufficient flammable fluid to pose a threat to vehicle occupants or the vehicle itself, and their small, bulky shapes provide difficulties in providing protection using the typical flat panel designs disclosed by Bennett. Some such components, such as the oil pan, may rupture and discharge flammable fluids due to the internal destruction of the engine, which is typically accompanied by the fracturing and penetration of the connecting rods through the oil pan. This scenario is very common in automobile racing in addition to highway occurrences. Other areas of a vehicle, such as the vehicle's engine compartment hood, exhibit damage in front end crashes not discussed by Bennett, and provide an opportunity for the mounting of a powder panel variant suitable for protecting against engine compartment fires. Panel designs disclosed by Bennett only describe panel activation due to collision-induced impacts, as opposed to heat activation, such as resulting from a small pool fire established under the fuel tank which poses the risk of burning through the tank and dumping significant quantities of fuel to exacerbate the fire event. Other threats to a vehicle and its occupants exist after a collision in addition to the presence of a fire, such as the discharge of battery acid from a ruptured battery, which were not addressed by Bennett. This threat is compounded for the large battery compartments present with electric or hybrid vehicles. One-piece powder panels formed by a single extrusion process, such as disclosed and illustrated by Bennett, may provide a low cost means of forming such panels. Such a design may not result in a panel with optimal panel weight minimization. It may also compromise optimal breakage of the panel due the strength of the internal ribs formed within the panel, the strength of its attachment to the outer face (with its characteristic of inhibiting favorable crack propagation), and the less than optimal fracture behavior of the outer face. The outer face, the component which is desired to fracture considerably, may fracture to a lesser extent when it is made of the same material as the rest of the panel (due to the necessity of forming the panel in one piece from one material), the material having been chosen to meet other mounting and strength requirements of the overall panel design during normal operation.
In summary, it is desired to provide a design of the powder panel concept (with or without usage of dry chemical powders as extinguishants) that can provide protection for other previously undisclosed fire scenarios and component failures, such as brake cylinders, fuel pumps, oil pans, fuel system valves, attachments and other front and engine compartment impacts and fires. It is also desired to have the ability for such powder panels to be activated by excessive heat, such as is due to a burning fire in proximity to the panel. It is also desired that the powder panels provide protection against other threats to occupants and the environment due to vehicle impacts, such the rupture and release of dangerous and caustic chemicals such as battery acids. It is also desired that such panels be designed whereby the outer face can be optimally constructed to fracture sufficiently due the selection of proper brittle materials, and the ability to limit the attachment strength of the outer face to the internal panel ribs to minimize the inhibition of the desired crack propagation, to maximize outer face breakup and resultant powder discharge. No device has been demonstrated that incorporates these features for this application.